A conveyor system of this type for unloading only of bulk material from ships with the features described above is known from German Auslegeschrift No. 2,813,182. The conveyor system of this patent publication utilizes two separate conveyor belts in the boom and in the vertical leg member, so as to enable a pivotability or rotatability of the vertical leg with respect to the boom which is necessary to reach all areas in the interior of a ship. Between the upper end of the vertical leg and the outer end of the boom, the bulk material arriving on the conveyor belt in the vertical leg, must be transferred to the other conveyor belt traveling in the boom to the gantry. However, it is difficult to so design and construct the point of material transfer that the bulk material is properly and entirely transferred in all positions of the vertical leg relative to the boom. For this purpose, this conveyor system possesses, among other things, a bow-shaped or C-shaped guide surface for the conveyor belt in the vertical leg with a cover belt extending over the conveyor belt traveling in the boom. This design makes the vertical leg extensive and heavy.
In another known conveyor system of a similar design disclosed in German Pat. No. 1,274,987, a separate intermediate conveyor belt is arranged at the point of material transfer between the conveyor belt in the vertical leg and the conveyor belt in the boom. This arrangement reduces somewhat the dimensions of the vertical leg though, but provides two points of material transfer.
On account of these material transfer points, both of the above described conveyor systems can only operate in one direction, and are thus directed to only unload ships and are not capable of selectively loading and unloading ships.